CHEM 121 glossary
π electrons
The electrons held in π bonds, 2 per π bond, so 2 for each double bond (C=C, C=O, N=N). To count a conjugated system, add 2 for each double bond in the largest connected system; in this course lone pairs on O or N are not counted.
Benzoic acid: 6 ring π electrons + 2 from the conjugated C=O.
Example
Benzoic acid, , has 3 ring C=C and a C=O attached directly to the ring: 8 conjugated π electrons. The lone pairs on the oxygens are not counted.